This invention relates to fuel injection pumps for internal combustion engines and particularly to such pumps wherein injection timing is adjusted in accordance with the operating conditions of the engine.
In a fuel injected engine, particularly a compression ignition or diesel internal combustion engine, it is desirable to adjust the injection timing in accordance with the operating conditions of the engine. Adjustment of the injection timing is desirable in accordance with the operating speed of the engine, in particular injection timing should be advanced as engine speed is increased. In addition to the speed proportional adjustment of the injection timing, it is desirable to additionally have an advancement of the injection timing during initial engine operation until the engine has reached its normal operating temperature.
Devices have been known which automatically adjust the injection timing of a fuel injection pump in accordance with the operating speed of the engine. Such devices make use of a piston in a cylinder which is acted upon by pressure in opposition to a spring. The pressure supplied is proportional to the speed of the engine and upon increased speed of the engine moves the piston against the spring thereby advancing the timing of the fuel injection pump through a connection between the piston and the injection pump.
There have been prior art devices for advancing the timing of an engine when the engine is cold. Such a device is disclosed in German published patent application No. 1,143,675. The advancement mechanism disclosed in that application makes use of a pressure cylinder within which there are coaxially mounted two pistons. The inner piston, upon stopping of the engine, assumes a position which advances the fuel injection timing and remains in this position during the engine starting period, independent of the operating temperature of the engine. This prior art device acts independent of engine temperature and advances the injection timing, even when the engine is being started warm. In this event, the unwarranted advancement of the injection timing results in an unfavorable combustion process with rough and noisy engine operation.
It is therefore an object of the present invention to provide a new and improved apparatus for adjusting the injection timing of fuel injection pump.
It is a further object of the present invention to provide such an apparatus which advances the injection timing when the engine temperature is below the normal operating temperature.